Electrical grounding receptacle

ABSTRACT

An electrical grounding receptacle is provided with means to insure that, upon insertion of a conventional three-pronged plug, contact between the grounding prong and the grounding contact is made before any contact can be made to the power contacts. The structure includes female contact elements within a housing including a grounding contact that has a portion extending within an opening of the front face in which the plug blade is received while the power contacts are disposed entirely below their corresponding openings in the front face.

United States Patent Smith [451 Jan. 18, 1972 541 ELECTRICAL GROUNDINGFOREIGN PATENTS OR APPLICATIONS RECEPTACLE 935,199 11/1955 Germany......339/14 R [72] Inventor: Clarence M. Smith, Bridgeport, Conn. 1,147,2824/1963 Gennany ..339/ 14 R 73 A' :Wcstl 'ElectlC u P'ttl 1 Sslgnee g gzj r c mpg" 1 Primary Examiner-Marvin A. Champion AssistantExaminer-Robert A. Hafer Filed: P 1970 Attorney-A, T. Stratton, F. P.Lyle and Gordon H. Telfer 211' App]. No.2 26,197

' [57] ABSTRACT [52] US. Cl. ..339/14 R, 339/156 R An electricalgrounding receptacle is provided with means to [51] Int.Cl ..H0lr 3/06insure that, upon insertion of a conventional three-pronged [58] Fieldof Search ..339/14, 156, 192 plug, contact between the grounding prongand the grounding contact is made before any contact can be made to thepower [56] References Cited contacts. The structure includes femalecontact elements UNITED STATES PATENTS within a housing including agrounding contact that has a portion extending within an opening of thefront face in which the 2,970,286 1/1961 Modrey...; ..339/14 R lug bladeis received while the power contacts are disposed ,7 1 952 H 14 Rentirely below their corresponding openings in the front face. 3,066,27111/1962 Carlson. ....339/14 R 3,345,603 10/1967 Cohen ..339/ 176 2Claims, 3 Drawing Figures I I I I I I I I I r I l PATENTED m 1 8 m23;636;494

PRIOR ART FIG.3.

WITNESSES MENTOR Clarence M. Smith ELECTRICAL GROUNDING RECEPTACLEBACKGROUND OF THE INVENTION 1. Field of the Invention This inventionrelates to electrical receptacles, such as for convenience outlets, andparticularly to those for three-wire attachment and mating with athree-pronged plug wherein a grounding instrumentality is provided.

2. Description of the Prior Art Grounding receptacles are in widespreaduse, often in the form of duplex receptacles, that include provision forreceiving two blades of a plug that in use carry the electrical powerand a third blade for purposes of grounding the appliance or otherinsu'umentality to which the plug is connected. Such plugs andreceptacles generally provide greater safety than corresponding devicesthat only include the power blades and contacts. The configuration ofsuch plugs and receptacles is limited in that there are industrystandards establishing the general nature of the devices and limits onthe dimensions of various elements thereof. Such standards have beenadopted by various governmental agencies.

NEMA standard -15-1961 for Plugs and Receptacles- General Purpose, 125volts, arnperes, 2 pole, 3 wire, grounding type" is an example of anindustry standard for the type of receptacles to which the presentinvention is applicable.

It has been found in rare occurrences that, with a receptacle of thetype described that complies with the established standards, it ispossible for a user to insert a plug in such a peculiar manner thatcontact is made between the power prongs of the plug and the powercontacts of the receptacle before any contact is made between thegrounding prong of the plug and the grounding contact of the receptacle.This is despite the fact that the grounding blade of the plug isrequired to be at least 0.125 inch longer than the power blades of theplug. Thus a user may assume that the use of a three-pronged plug andmating receptacle provides a measure of safety which is in fact absent.The hazard is found most likely to occur when the plug is inserted in amanner that it is tilted away from the grounding contacts, particularlywith some slight lateral bending of the blades.

It is apparent that the above-mentioned hazard could be avoided bygreater restriction on the dimensions of the openings of the receptaclewithin which the plug blades are inserted, so as to more closely confinethem and require the user to insert the plug with all the blades morenearly perpendicular to the face of the receptacle. However, the abovereferred to standards establish minimum dimensions for these openings,as well as maximum dimensions, and even with such minimum dimensionsthere is a possibility of the described hazard.

By way of further background, reference may be made to Howells U.S. Pat.No. 3,032,736, May 1, 1962, for a description of some receptacles of thegeneral type to which the present invention applies.

SUMMARY OF THE INVENTION This invention provides a receptacle thatavoids the hazard of having hot plug contact made before groundingcontact is made in the three-wire grounding-type receptacles, includingthose that satisfy prevailing industry standards, with only a modestchange in structural design that can be readily and economicallyimplemented by the manufacturer and without imposing any higher degreeof care on the part of the user or other disadvantage.

The invention provides these advantages in a receptacle having a housingthat includes a first portion of insulating material in which arecontained a pair of mutually insulated power contact elements. Thehousing also includes means for containing a grounding contact,typically connected with a metal yoke that provides ultimate connectionto anelectrical ground. The housing has a front face with openingstherein communicating to the contained contacts and for receiving theblades of a mating plug. The power contact elements are disposedentirely below the openings in the front face of the housing while thegrounding contact includes a portion that extends within the opening ofthe front face so that insertion of a plug at any angle requires initialcontact with the grounding contact of the receptacle.

In a conventional receptacle, the grounding contact is a U- shapedelement that fits within a pocket formed by the insulating portion ofthe housing and-a metal yoke in a manner such that the grounding contactis in electrical connection with the yoke at the bottom of the U-shapedportion. In accordance with this invention, one leg of the U-shapedgrounding contact is made elongated to extend within the front faceopening. Preferably, this extended portion of the grounding contactterminates at approximately the plane of the exposed front face.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a partial cross-sectionalview of a receptacle in accordance with the prior art, with a matingplug, to illustrate the problem to which the present invention isdirected;

FIG. 2 is a perspective view of a receptacle in accordance with thepresent invention; and

FIG. 3 is an elevation view, partly in cross section, of the structureof FIG. 2 with a mating plug illustrated to show solution of the problemto which the invention is directed.

DESCRIPTION OF THE PREFERRED EMBODIMENT By way of further background tothe present invention, reference is made to FIG. 1 to illustrate how aproblem can arise in the use of prior art receptacles. Such a receptacle10 includes an insulating housing 12 containing power contact elements14 communicating with screw terminals 16 for wire attachment. Thereceptacle 10 also contains a U-shaped grounding contact 18 inelectrical connection with a metal yoke 20. Upon the insertion of athree-pronged plug 22 having power blades 24 and a grounding blade 26,it is possible to make initial contact with power contacts 14 of thereceptacle 10. While such manner of insertion is neither usual norfrequent, it does expose the user to an obvious risk which is desirablyavoided.

In a device in accordance with this invention, as shown in FIGS. 2 and3, the receptacle 30 includes a housing that comprises a first portion32 of insulating material which contains mutually insulated powercontacts 34 (only one of which is shown) in a manner that they connectwith screw terminals 36 laterally disposed for connection with wires.The receptacle 30 also includes a generally U-shaped grounding contactmember 38 in electrical connection with a metal yoke 40. The yoke 40effectively forms part of the housing and with insulating portion 32provides a pocket 42 in which the contact member 38 is contained.Openings 44 and 48 in front face 50 of the housing insulating portion 32provide plug access with the power contacts 34 and ground contact 38,respectively. For simplicity in the drawing, some details ofconventional elements in the structure are omitted. It is particularlydesirable that the invention be applicable to otherwise standardconfigurations with only slight change. The invention is shown embodiedin a duplex receptacle, only one-half of which will be specificallydescribed. While the general configuration of receptacle 30 isconventional, this is merely by way of example as the invention may becarried out in other forms.

The improvement which is sought is provided by having a first leg 38A ofthe U-shaped ground contact 38 extended to within the opening 48provided in the front wall or face 50 of the receptacle 30. The powercontacts 34 are disposed below the openings 44 in the front face 50. Aninserted plug 22 (FIG. 3) is thus required to make contact betweenground blade 26 and ground contact 38 before hot contact is made betweenblades 24 and contacts 34.

In the example shown, the receptacle 30 includes a feature shown inHowells U.S. Pat. No. 3,032,736, in that opening 48 for the groundcontact is in the form of an elongated slot with a cross section'that isarcuate on one side and open on the other side. lnsulating member 32may, if desired, have a wall at the illustrated open side of opening 48.However, such a wall is subject to breakage and is preferably avoided.The invention is, of course, applicable to receptacles with or withoutsuch a wall.

The extent of leg 38A of ground contact 38 may be varied in accordancewith the extent of thepower contacts 34, the size of openings 44 and 48(in relation to plug blades 24 and 26), as well as other factors, whilestill performing its intended function. Conveniently, ingenerally-standard receptacles as described, leg 38A may extend toapproximately the same plane as the front face 50 while the powercontacts 34 terminate below or at the plane of the innermost wallsurface 51. Typically, therefore, there is a difference of about 0.25inch between the extremities of elements 38A and 34 in devices inaccordance with the exemplary embodiment of the invention.

I claim:

1. An electrical grounding receptacle comprising: a housing comprising afirst portion of insulating material and containing a pair of mutuallyinsulated power contact elements and a grounding contact; said housinghaving a front with a plurality of openings therein to receive blades ofa plug and connect said blades with said grounding and power contactelements;

said power contact elements being entirely disposed below said frontface; said grounding contact having a' portion thereof extending withinan opening in said front face so insertion of a plug at any anglerequires initial contact with said grounding contact; said housing alsocomprising a metal yoke which with said first portion forms a pocket forcontaining said grounding contact in electrical connection with saidyoke; said grounding contact having a generally U-shaped structure withsaid portion extending within an opening of said front face being afirst leg of said U-shaped structure, said first leg being adjacent anupstanding portion of said yoke and effectively restricting, to anextent greater than said first portion and said metal yoke alonejsaidopening for receiving a plug blade, said U-shaped structure having asecond leg adjacent said first portion of said housing and shorter thansaid first leg.

2. The subject matter of claim 1 wherein: said first leg has anextremity terminating substantially at the plane of said front face.

I I! i i

1. An electrical grounding receptacle comprising: a housing comprising afirst portion of insulating material and containing a pair of mutuallyinsulated power contact elements and a grounding contact; said housinghaving a front with a plurality of openings therein to receive blades ofa plug and connect said blades with said grounding and power contactelements; said power contact elements being entirely disposed below saidfront face; said grounding contact having a portion thereof extendingwithin an opening in said front face so insertion of a plug at any anglerequires initial contact with said grounding contact; said housing alsocomprising a metal yoke which with said first portion forms a pocket forcontaining said grounding contact in electrical connection with saidyoke; said grounding contact having a generally U-shaped structure withsaid portion extending within an opening of said front face being afirst leg of said Ushaped structure, said first leg being adjacent anupstanding portion of said yoke and effectively restricting, to anextent greater than said first portion and said metal yoke alone, saidopening for receiving a plug blade, said U-shaped structure having asecond leg adjacent said first portion of said housing and shorter thansaid first leg.
 2. The subject matter of claim 1 wherein: said first leghas an extremity terminating substantially at the plane of said frontface.